This invention relates to the testing of magnetic workpieces which include a permanent magnet member to determine their respective magnetic field strength, and more particularly to the testing of precision components for a miniature watch motor or the like.
In watch motors, the permanent magnet rotor must have sufficient magnetic strength in order to maintain minimal starting torque for advancing the rotor, which in turn advances the seconds, minutes and hours indicators of the watch. With the magnetic strength of the rotor/axle assembly being optimum the efficiency of the watch motor is increased thereby prolonging battery lifetime. Therefore, it is necessary to determine the magnetic strength of the motor magnet system in order to insure that the magnetic strength thereof is in a predetermined range to insure the above condition. Also, wide variations in magnetic strength of the rotor and rotor assembly will produce similar variations in product yield, as the motor magnet system is reasonably sensitive to magnetic field strength changes.
Thus, a need exists to provide an efficient and accurate test apparatus for measuring the magnetic strength of the rotors in the most economical manner.